A rate-based flow control mechanism for avoiding congestion

The rate-based flow control mechanisms for the Available Bit Rate(ABR)service are used to share the available badwidth of a bottleneck switch connected to a bottleneck link fairly and reasonably among many competitive users,and to maintain the buffer queue length of the witch at a desired level in order to avoid congestion in Asynchronous Transfer Mode(ATM)networks.In this Paper,a control theoretic approach that uses a Deadbeat-Response(DR) controller to the desing of a rate-based flow control mechanism is presented.The mehanism has a simple structure and is robust in the sense that its stability is not sensitive to the change of the number of active Virtual Connections(VCs),Simulation results show that this mechanism not only ensures fair share of the bandwidth for all active VCs regardless of the nmuber of hops they traverse but also has the advantages of fast convergence ,no oscillation,and high link bandwidth utilization.     

Performance analysis of dynamic load balancing algorithms with variable number of processors

In modern parallel adaptive mesh computations the problem size varies during simulation. In this study we investigate the comparative behavior of four load balancing algorithms when the number of processors is dynamically changed during the lifetime of a multistage parallel computation. The focus is on communication and data movement overheads, total parallel runtime and total resource consumption. We demonstrate the main ideas for the case of six adaptive mesh refinement (AMR) applications with different kinds of growth patterns. The results presented are for a 32 processor Intel cluster connected by Ethernet.     

Performance analysis of a new energy-efficient variable supply pressure electro-hydraulic motion control method

Electro-hydraulic actuation is used in many motion control applications due to its high power density, excellent dynamic response and good durability. However fluid power actuation has been shown to be very energy inefficient, with an average efficiency for fluid power systems across all industries of 22% in the USA. This is a very significant problem, given that 3% of the energy used by mankind is transmitted in this way.The key challenge for researchers is to reduce energy losses in hydraulic actuation systems without increasing weight, size, and noise, and without reducing speed of response. Conventional high performance electro-hydraulic motion control systems use a fixed supply pressure with valve-controlled actuators (FPVC). This is inherently inefficient due to the need to use a valve to throttle the flow required by each actuator in the system down to match its load pressure. In this paper, a new load-prediction based method is proposed, in which the supply pressure is varied to track the pressure required by any actuator branch. By implementing this model-based approach using a high response servomotor-driven pump, it is shown that the dynamic response remains excellent. The load model not only allows feedforward control for servomotor speed based on the motion demand, but also feedforward for the control valves to supplement conventional proportional-integral feedback control.The new variable supply pressure valve-controlled (VPVC) method is investigated in simulation and experimentally using a two-axis hydraulic robot arm supplied by an axial piston pump. The performance has been rigorously compared with the same robot arm using a fixed supply pressure and proportional-integral joint position control. Experimental results showed that up to 70% hydraulic power saving was achieved, and that the dynamic tracking errors for VPVC were about half that for FPVC as a result of using feedforward control.     

First-order rate-based flow control with dynamic queue threshold for high-speed wide-area ATM networks

In this paper we present a new rate-based flow control scheme for ATM ABR services and analyze its performance. The proposed algorithm, which we refer to as first-order rate-based flow control (FRFC) is the most simple form of queue-length-based flow control. The asymptotic stability, the steady-state throughput, queue length and fairness, and the transient behavior are analyzed for the case of multiple connections with diverse round-trip delays. We also consider a novel approach to dynamically adjust a queue threshold in the FRFC according to the changes in the available bandwidth, and the arrival and departure of connections. Simulations show that the simple FRFC with dynamic queue threshold (DQT) effectively maintains high throughput, small loss and a desired fairness in these dynamic environments and is a promising solution for ABR flow control in ATM networks.     

Performance analysis of a folding flow micromixer

The performance of a folding flow micromixer in the Stokes flow regime is investigated computationally and experimentally. Consistency with a previously derived general scaling relation is demonstrated and the geometric parameters in the scaling relation are determined for this mixer. Measured data from a second similar mixer are correctly predicted using the scaling relation, thus showing that the approach allows quantitative prediction of mixing. This paper focuses on the errors associated with such predictions. Basic errors, expressed as variations in the standard deviation of the concentration profile, were estimated to be −10% for the computation and −30% for the experiment at the highest values of Péclet number considered. It is shown that this experimental error was mostly due to depth averaging of the spectroscopic technique used for concentration measurement at the high Péclet numbers. However, extra uncertainty is associated with chip fabrication tolerances and this was investigated further. Measurements at the outlet of nine different mixer chips of notionally identical design revealed variations in mixing of ±26%. This variation was attributed to misalignment of the glass layers determining the geometry of the mixer in the chip. Thus, the combination of measurement error and misalignment means predictions of the concentration standard deviation for the mixer may get non-uniformity wrong by up to 50%. Ensuring a required uniformity, however, simply requires adding a few further elements to the mixer to allow for this uncertainty. Application of the scaling relation to mixer design is highlighted by a discussion of the options available for improving the performance of the experimental mixer.     

Analysis of a rate-based feedback control strategy for long haul data transport

Digital communication has become fast enough so that the speed of light has become a bottleneck. For example, the round trip transcontinental [USA] delay through a fiber link is approximately 0.04 s; at 150 Megabit/s, a source needs to transmit approximately 8,000,000 bits during one round trip time to utilize the bandwidth fully. As the service rates of queues get large, the time scales of congestion in those queues decrease relative to the round trip time, making the dual goals of keeping buffers small and utilizations high even more difficult to achieve. In this paper we analyze a class of delayed feedback schemes that achieve these goals despite propagation delays and regardless of network rates. We analyze the delayed feedback schemes as a system of delay-differential equations, in which we model the queue-length process and the rate at which a source transmits data as fluids. We assume that a stream of acknowledgements carries information about the state of a bottleneck queue back to the source, which adapts its transmission rate according to any monotone function of that state. We show stability for this class of schemes, in that their rate of transmission and queue length rapidly converge to a small neighborhood of the designed operating point. We identify the appropriate scaling of the model's parameters, as a function of network speed, for the system to perform optimally: with a deterministic service rate of μ at the bottleneck queue, the steady state utilization of the queue is and steady state delay is . We also describe the transient of behavior of the system as another source suddenly starts competing for the bandwidth resources at the bottleneck queue. This work directly applies to the adaptive control of Frame Relay and ATM networks, both of which provide feedback to users on congestion.     

Localized online learning-based control of a soft redundant manipulator under variable loading

ABSTRACT

Soft robots are inherently compliant and manoeuvrable manipulators that can passively adapt to their environment. However, in order to fully make use of their unique properties, accurate control should still be maintained when affected by external loading. Commonly used model-based approaches often have low tolerance to unmodelled loading, resulting in significant error when acted on by them. Therefore, in this study we employ a nonparametric learning-based method that can approximate and update the inverse model of a redundant two-segment soft robot in an online manner. The primary contribution of this work is the application and evaluation of the proposed framework on a redundant soft robot. With the addition of redundancy, a constrained optimization approach is taken to consistently resolve null-space behaviour. Through this control framework, the controller can continuously adapt to unknown external disturbances during runtime and maintain end-effector accuracy. The performance of the control framework was evaluated by tracking of a 3D trajectory with a static tip load, and a variable weight tip load. The results indicate that the proposed controller could effectively adapt to the disturbances and continue to track the desired trajectory accurately.     

pH值系统变论域模糊控制器的设计及性能分析

针对pH值非线性控制系统,设计了一种实时简化变论域模糊控制器.将变论域思想与实时模糊推理策略相结合:一方面论域随着误差的减小而收缩,而论域的收缩相当于控制规则的增加,从而增加了控制精度;另一方面采用实时模糊推理方法,即对于一个二入一出的模糊控制器,一次推理过程中最多只激活4条控制规则,在控制的过程中只考虑这4条控制规则.这2种思想的结合使得控制规则的设计大大简化,可以采用批处理的方式设计控制器,不仅加快了系统的动态响应,也提高了控制精度.仿真结果证实了这种控制方法的有效性.     

Case study on rate-based traffic control of industrial networks employing LonWorks

Industrial communication networks have attracted much attention in the area of decentralized control systems for factory automation and computer integrated manufacturing. This paper investigates the rate-based traffic control of industrial communication networks employing LonWorks to improve the performance measures of throughput, fairness and error rates. For this purpose, we utilized feedback channel information through an additional network-monitoring node and made the overall system closed-loop. We demonstrate an improved performance of the controlled network system through experimentation upon an implemented lab-scale network system.     

Optimizing a multiserver queuing system with a variable number of servers

A multiserver Poisson queuing system with losses, with a variable number of servers, and an additive quality functional is investigated. All major characteristic of the system are obtained in an explicit form. __________ Translated from Kibernetika i Sistemnyi Analiz, No. 4, pp. 92–101, July–August 2007.     

Performance analysis of reset control systems

In this paper we present a general linear matrix inequality‐based analysis method to determine the performance of a SISO reset control system in both the ??₂ gain and ??₂ sense. In particular, we derive convex optimization problems in terms of LMIs to compute an upperbound on the ??₂ gain performance and the ??₂ norm, using dissipativity theory with piecewise quadratic Lyapunov functions. The results are applicable to for all LTI plants and linear‐based reset controllers, thereby generalizing the available results in the literature. Furthermore, we provide simple though convincing examples to illustrate the accuracy of our proposed ??₂ gain and ??₂ norm calculations and show that, for an input constrained ??₂ problem, reset control can outperform a linear controller designed by a common nonlinear optimization method. Copyright © 2009 John Wiley & Sons, Ltd.     

Performance analysis of a virtual circuit protocol with local control

In many current packet switching networks, packets are transmitted sequentially by means of so-called virtual circuits. In this paper, a queueing network model for a virtual circuit with local buffer size constraints and blocking at the intermediate nodes is derived and analysed. The analysis is based on the decomposition of the fixed virtual route into its individual links. Each hop is modelled as a closed BCMP queueing network. The introduction of the steady-state blocking probability p as the characterizing parameter of the interface between two consecutive links permits the recursive computation of important design parameters, such as throughput, utilization, and mean transmission time. A modified rejection probability, introduced to describe the behaviour at the interface more accurately, supports the previous results.     

FastICA和RobustICA算法在盲源分离中的性能分析

首先简单介绍了FastICA和RobustICA这两种目前最为常用的盲源分离两种算法, 并对这算法的目标函数以及优化算法进行了分析研究, 进一步对这两种算法的稳健性及算法复杂度等方面的性能进行分析比较。总的来看, RobustICA算法的综合性能要优于FastICA算法。     

Stability analysis of a mobile manipulator under force control

Coordination of multiple mobile agents in general requires interactions between an agent and its external, e.g. another agent or its environment. It is therefore essential for each agent to maintain its stability while interacting with the external. In this study we analyze the stability of a mobile manipulator under force control. A lumped linear mass model is employed due to its simplicity and expressivity. First, a mobile platform and a manipulator with an environment are modeled separately. Both are then combined to yield a mobile manipulator model whose behavior is examined under various force control laws.     

MCMC-based particle filtering for tracking a variable number of interacting targets

We describe a particle filter that effectively deals with interacting targets, targets that are influenced by the proximity and/or behavior of other targets. The particle filter includes a Markov random field (MRF) motion prior that helps maintain the identity of targets throughout an interaction, significantly reducing tracker failures. We show that this MRF prior can be easily implemented by including an additional interaction factor in the importance weights of the particle filter. However, the computational requirements of the resulting multitarget filter render it unusable for large numbers of targets. Consequently, we replace the traditional importance sampling step in the particle filter with a novel Markov chain Monte Carlo (MCMC) sampling step to obtain a more efficient MCMC-based multitarget filter. We also show how to extend this MCMC-based filter to address a variable number of interacting targets. Finally, we present both qualitative and quantitative experimental results, demonstrating that the resulting particle filters deal efficiently and effectively with complicated target interactions.     

Performance evaluation of a single-stage two-product manufacturing system operating under pull-type control

This paper presents a model to analyze a manufacturing system that is operating under pull-type control. A Markovian polling model with finite queues is devised to represent the manufacturing system and studied under three cyclic service policies: exhaustive, gated, and a type of limited policy. These polling models are solved by two different methods: an exact approach that requires the complete characterization of the system as a Markov chain and a decomposition approach that reduces the size of the Markov chain. A set of numerical experiments show that the decomposition approach is quite accurate in estimating system performance measures.     

Performance analysis of a hybrid system under quality impact of returns

In this paper we analyze a hybrid system that meets the demand with remanufactured or new products. In the remanufacturing stage there are uncertainties in the quality of remanufactured products, return rates and return times of returned products. These uncertainties affect raw material order quantities, processing times and material recovery rates. In the study returned products are classified by considering quality uncertainties. According to this classification remanufacturing processing times, material recovery rates, remanufacturing costs and disposal costs are determined. In order to analyze the effect of uncertainties in return quality a simulation model is constructed by using the ARENA simulation program. Our analysis denotes that under different cost scenarios quality based classification of returned products brings significant cost savings. The numerical analysis indicates that a cost improvement of more than 8% is achieved when return rates are high.     

Performance analysis of a retransmission control algorithm for local area networks

Algorithms for the control of the transmission procedure in multiaccess schemes must ensure simplicity in the implementation, stability of the system operation and high efficiency for all traffic conditions. A control algorithm suitable for slotted multiaccess schemes based on monitoring the channel transmissions is proposed. A model is presented and the algorithm is analysed in detail. The performance of the algorithm is evaluated, and comparisons are made with multiaccess protocols.